1. Field of the Invention
The invention relates to a method of modifying a turbocompressor, to a turbocompressor modified according to this method, and to the use of the turbocompressor so modified.
2. Brief Description of the Related Art
During the start-up of a turbocompressor, the compressor, on account of the stage kinematics at low speed, is not able to deliver the entire delivery quantity of the volumetric inlet flow against the pressure imposed by the load. It is also problematical at underspeed of a turbocompressor that the volumetric flow in the rear compressor stages turns out to be markedly smaller than corresponds to the design of the cross sections of flow. Thus, on the one hand, the enthalpy build-up is displaced into the front compressor stages, in which there is therefore an increased tendency of the compressor flow to separate. On the other hand, obstruction of the cross sections of flow potentially occurs in the rear compressor stages, which further increases the pressure build-up in the front compressor stages. It is therefore known to arrange blow-off lines at intermediate stages of turbocompressors, these blow-off lines being capable of being shut off. During the acceleration of the turbocompressor, these blow-off lines are opened. Thus some of the mass flow delivered into the front compressor stages is drawn off, and only a partial mass flow is admitted to the rear compressor stages. It is ensured that the axial velocity of the flow in the front compressor stages is high enough in order to prevent a flow separation, whereas the axial velocity in the rear compressor stages does not achieve any critical values.
In the course of the service life of turbocompressors over several years, progress in the fields of aerodynamics and production technology permits improvements in output through the use of modern blades. Use is made of these possibilities by existing turbocompressors, for example of gas turbosets, being retrofitted with improved blades. The effect of such retrofitting with improved blades is an increased volumetric intake flow and thus an increased nominal mass flow of the compressor, thereby also resulting in a higher pressure ratio with an unchanged load, for example a turbine, arranged downstream of the compressor.